This invention relates to a rotary electrical machine of the type which comprises a rotor and a stator on which electrical windings are formed.
The invention also proposes a method of making a rotor and a stator for a rotary electrical machine.
As is known, rotary electrical machines comprise a rotor and a stator on each of which an electrical winding may be formed.
The rotary electrical machine may be an alternator which converts rotary motion of the rotor into an electric current. The electrical machine may also be a motor which converts an electric current flowing through a winding of the rotor into rotational movement of the is rotor. The machine can be reversible and can thereby convert mechanical energy into electrical energy and vice versa.
Each electrical winding consists of a winding of at least one electrically conductive element which is coated with a layer of electrically insulating material. In transverse cross section, a winding is thereby formed in which portions of the electrically conductive element are juxtaposed horizontally and vertically.
As is known, the stator of a rotary electrical machine comprises a body which is provided with a set of axial or helical internal slots open radially and open axially. Such slots can be seen for example in the document FR-A-2 603 429 (U.S. Pat. No. 4,908,541). Conventionally, the body is of metal and consists of a stack of metal laminations. Each slot receives a set of portions of one or more conductive elements of a coil of a stator winding. The coil includes axial strands which are received in the slots and which are joined together by transverse strands in the form of loops which constitute heads of the winding, which are also called wings.
In general, the alternator is of the three-phase type, and the stator has three windings. In another version the alternator is of the six-phase type.
During manufacture of the stator, the axial strands of the coated conductive elements are compressed transversely within the slots, so that they fill the latter more fully, and they are then held in position by means of a slot closure element, for example.
In order to ensure optimum functioning of the rotary electrical machine, it is preferable that the winding should, with the stator, form a sufficiently rigid block, in particular to limit vibrations and noise, and to do so throughout the whole working life of the rotary electrical machine. The block must however be flexible enough to limit magnetic noise.
The known manufacturing method consists in impregnating the winding thus formed with a varnish, so as to stiffen it and to join it to the stator.
The impregnation can be obtained by immersing the stator in a bath of varnish, or by causing varnish to flow over and between the axial and transverse strands.
In order to cause the varnish to set, the stator which is equipped with the winding is heated in a stove to a sufficiently high temperature.
However, the viscosity of the varnish, and the contact between certain portions of the strands of the winding, do not permit the varnish to fill in an optimum manner some of the interstice that exist.
Such a method has a number of drawbacks.
The partial impregnation of the winding does not allow the conductive elements to form a rigid enough block. The mechanical and vibrational strength of the stator is not optimised. In consequence, the noise emitted by the machine is not minimal.
The said method is long, as the impregnation of the winding and setting of the varnish lasts for several tens of minutes. In addition, the method is difficult to control and calls for expensive installations such as stoves which consume large quantities of energy. It also causes polluting vapour to be emitted, especially during heating of the varnish.
The dimensional tolerances in the stator, especially in the wings, are large. In this connection, the positioning of the transverse strands of the electrically conductive element is not correctly controlled. They can shift between the instant at which the axial strands are received in the slots in the stator body, and the instant at which the varnish becomes set. It is therefore necessary to provide large operating clearances around the wings of the stator, so that, firstly, the transverse strands will not rub on the carcass of the rotary electrical machine, which would cause wear in the insulating layer and then a short circuit, and secondly, any risk of fracture of the transverse strands by the rotor during its rotation is avoided.
The movement of the transverse strands also causes the density of the wings to be reduced.
In order to reduce the risk of short circuit between the conductive element and the stator body, a leaf of electrically insulated material is interposed between each wall that defines a slot and the adjacent axial strands of the conductive element that lie in that slot.
The reduction in the risk of short circuiting between the conductive element and the stator body can also be obtained by means of a protective layer such as an epoxy layer. This protective layer is interposed between each wall that defines a slot and adjacent axial strands of the conductive elements situated in that slot.
In order to ensure good mechanical and vibrational strength in the winding, it is preferable that it be immobilised with respect to the stator body, that is to say the leaf of insulating material should be joined to the wall which defines the slot and to the axial strands with which it is in contact. Thus, in general, holes are formed in the leaf in such a way as to enable varnish to pass through them so as to infiltrate between the wall defining the slot and the insulating leaf.
Heating of the stator hardens the varnish, and consequently immobilises the insulating leaf with respect to the axial strands with which it is in contact, and with respect to the slot.
However, it frequently happens that the amount of varnish which enables these joints to be made, especially that which infiltrates between the wall defining the slot and the insulating leaf, is insufficient to ensure fastening of those elements. The vibrations set up by their movement with respect to the stator body increases noise in the rotary electrical machine and reduces its output.
Where the quantity of varnish is insufficient between the wall defining the slot, the leaf of insulating material and the conductive element, heat transfer is reduced, which causes the output of the rotary electrical machine to be reduced.
On the other hand, where there is too much varnish, the general stiffness of the wires with the stator body is not optimum, and this results in magnetic noise induced by the magnetic forces.
In addition, the stiffness of the varnishes currently employed varies with temperature. Thus, the higher the temperature of the varnish, the weaker is the magnetic noise emitted by the rotary electrical machine.
In consequence, the known method does not permit manufacture of a stator which ensures optimum operation of the rotary electrical machine.
The winding of the rotor of the rotary electrical machine is generally formed in a winding body of electrically insulated plastics material, which consists of an annular element having a U-shaped axial half section as can be seen for example in FIG. 1 of the document FR-A-2 603 429 mentioned above.
The winding body guides the electrical conductive element while it is being wound. However, it frequently happens that the transverse wings of the winding body move slightly apart, thereby causing poor winding. The electrically conductive element can take the form of transverse wings overlaid with petals. During transport before impregnation of varnish, there can also occur partial radial displacement of certain portions of the electrically conductive element of the winding which moves the flanks of the winding body apart and causes it to become wider. Thus, when the winding is to be interposed between the two pole wheels, this widening effect is compacted, which involves the danger of destruction of the electrically insulating coating, in particular that of the axial strands of the conductor, thereby creating contacts between them which cause a loss of resistance. In addition, the radial widening effect can be detrimental to the contact between the core on which the winding is mounted and the two pole wheels, which creates a parasitic air gap of the core with respect to the pole wheels and consequently a loss of power and output of the rotary electrical machine.
Varnish is then deposited on the winding, and is then hardened, thereby permanently perpetuating the faults in the winding.
In addition, the winding body, which is generally of plastics material, forms a thermal screen between the winding, the core, and the pole wheels, which is detrimental to transfer and dissipation of the heat produced by passage of the current in the electrically conductive element, and it thereby reduces the output of the rotary electrical machine.
In particular, the varnish enables the mechanical strength of adjacent portions of the electrically conductive element to be achieved between them, and fastens the winding body on the core and pole wheels.
With a view to providing a remedy for these disadvantages, the invention proposes a rotary electrical machine of the type which comprises at least one member on which at least one electrical winding is formed, the winding comprising at least one electrically conductive element which is wound in such a way as to form the winding and which is coated with at least one layer of electrically insulating material, characterised in that, prior to the winding step, the coated conductive element is clad with a connecting layer consisting of at least one connecting material that joins together adjacent portions of the coated electrically conductive element, in that an electrically insulating leaf is interposed between the winding and the member on which the winding is formed, and in that the insulating leaf comprises an electrically insulating structural element, on at least one of the faces of which a second connecting material is applied at least partially, whereby to join the insulating leaf to the winding and/or the member on which the winding is formed.
Thanks to the invention, optimum filling is obtained in the interstices that exist between the strands of the winding and electrical insulation between the winding and the member on which the winding is mounted.
The second connecting material reinforces the filling of the said interstices and/or the joint with the said member, so that the performance of the machine is improved.
Preferably, the structural element is at least partially impregnated, that is to say coated on its two faces, by the second connecting material, to give maximum optimisation such that good mechanical and vibrational strength of the winding are obtained. The winding is thus immobilised with respect to its associated member, while forming a block which is robust without any relative movement between its strands in the electrically conductive elements and the said associated member.
In addition, the insulating leaf is perfectly immobilised and can be very thin, and no hole need be provided in the latter, so that the material in the electrically conductive element, and the performance of the machine, can be increased.
Preferably, the insulating leaf is thin and is thermally conducting, so as to evacuate heat effectively to the appropriate member which is a thermal conductor, thereby optimising the performance of the machine even more.
The said connecting material is chemically and thermally compatible with the first connecting material.
According to further features of the invention:
the second connecting material is identical to the first connecting material, for the most intimate possible cooperation between these latter and improved temperature control; the connecting elements react in the same way;
the structural element is a leaf of electrically insulating paper;
the structural element is made of electrically insulating cloth;
at least one of the connecting materials comprises a polymer;
the polymer is of the thermosetting type, for greater reliability and longer useful life of the electrical machine;
the polymer is of the thermoplastic type, the melting point of which is higher than the maximum working temperature of the rotary electrical machine;
the member on which at least one winding is formed is a stator;
the member on which at least one winding is formed is a rotor;
the machine is an alternator;
the machine is an electric motor.
The invention also proposes a method of making a member for a rotary electrical machine on which there is formed at least one electrical winding comprising at least one electrical conductive element which is wound in such a way as to form the winding, and which is coated with at least one layer of electrically insulating material, of the type which includes a step of winding the conductive element in such a way as to form the electrical winding, characterised in that prior to the winding step, the coated conductive element is clad with a connecting layer consisting of at least one connecting material that joins together two adjacent portions of the coated electrically conductive element, in that the winding step is followed by a step of changing the state of the connecting material so as to cause it to soften or melt whereby it fills, at least partially, the interstices that exist between the adjacent portions of the conductive element, and so as then to cause it to solidify once again, whereby to join together the adjacent portions of the conductive element, in that an electrically insulating leaf which comprises a structural element at least partially coated or impregnated with a second connecting material, is interposed between the winding and the member on which the winding is formed, and in that, during the step of changing state, the second connecting material is softened or melted and is then once again solidified, and joins together the insulating leaf and adjacent portions of the conductive element and/or the member on which the winding is formed.
According to further features of the method of making a member of a rotary electrical machine:
at least one of the first or second connecting materials comprises a polymer, and the step of changing state causes its polymerisation to take place;
in association with the step of changing state, the winding is formed into a predetermined shape by means of a shaping tool, which exerts a force on at least one zone of the winding in such a way as to deform it;
the winding is given its predetermined shape by means of a shaping tool which exerts at least a radial force on at least one axial annular zone of the winding, so as to deform it and to determine at least one diameter of the winding;
the winding is put into its predetermined shape by means of a shaping tool which exerts an axial force on at least one radial annular zone of the winding, so as to deform it and to determine the axial dimension of the winding;
the winding is given its predetermined shape by means of a shaping tool which exerts a force on a peripheral annular face of the winding in such a way as to give it a convex form;
the winding is put into its predetermined shape by means of a shaping tool which deforms the winding in such a way as to form at least one notch on a peripheral face, in particular a recess formed on an external annular peripheral face to permit passage of at least one axial tooth of a pole wheel, where the member is a rotor and the rotary electrical machine is an alternator;
the step of changing state comprises a step of heating the connecting layer to a hardening temperature higher than or equal to the melting point of the first connecting material, whereby to cause it to melt so that it fills at least partially the interstices that exist between the adjacent portions of the conductive element, and a cooling step in the course of which the first connecting material solidifies once again and joins together the adjacent portions of the conductive element;
during the heating step, the second connecting material which coats or impregnates the structural element of the leaf is brought to a temperature higher than its melting point, and, during the cooling step, the second connecting material solidifies once again and joins together the insulating leaf and adjacent portions of the conductive element and/or the member on which the winding is formed;
in association with the cooling step, the winding is formed into a predetermined shape by means of a shaping tool which exerts a force on at least one zone of the winding in such a way as to deform it;
the heating step consists in heating the electrically conductive element at least partially, by Joule effect, in such a way as to bring the temperature of at least one of the connecting materials to a temperature higher than or equal to its hardening temperature;
the heating step consists in heating the electrically conductive element at least partially by induction, by placing the winding in a magnetic field whereby to bring the temperature of at least one of the connecting materials to a temperature higher than or equal to its hardening temperature;
the heating step consists in heating at least one of the connecting materials at least partially by stoving, whereby to bring the temperature of at least one of the connecting materials to a temperature higher than or equal to its hardening temperature;
the step of changing state consists in projecting a reactive substance such as alcohol on at least one of the connecting materials, whereby it causes it to soften or melt and then once again causes it to solidify.
According to a further feature, the heating step is preceded by a step of preheating the appropriate member so as to reduce the temperature gradients that appear during the heating operation.
In all cases, the temperature attained during the preheating phase in the region of the appropriate winding will be able to be lower than or equal to the hardening temperature of the connecting element.
Because of the step of preheating, the electrically insulating leaf may be made very thin while being thermally conductive, which further minimises the size of the rotor and/or enlarges the winding, as well as optimising still further the transfer of heat to the relevant member while assuring optimum connection of the adjacent portions of the electrically conductive element.
In all cases of course, the electrically insulating layer is so (chosen that it will not be destroyed during the heating and/or preheating step. The same is true for the electrically insulating leaf.